Traditionally, the input impedance matching of low noise amplifier is transformed through inductor feedback. For example, “A 1-GHz BiCMOS RF front-end integrated circuit”, published in IEEE Journal of Solid-State Circuits, 1994, described that the amplifier circuits were designed through the method of inductor feedback, and the methodology was extensively used to design different low noise amplifiers. In addition, “A 3-10 GHz low-noise amplifier with wideband LC-ladder matching network”, published in IEEE Journal of Solid-State Circuits, 2004, also demonstrated that the method of inductor feedback was adopted for generating input impedance matching to 50 ohm to gain low noise figure.
Furthermore, input impedance matching for forming ultra-wideband could be transformed through the passive filter theory, and a plurality of inductors are used to reach impedance matching for ultra wideband. For instance, “An ultra-wideband CMOS low-noise amplifier for 3.1-10.6 GHz wireless receivers”, published in IEEE Journal of Solid-State Circuits 2004, showed that it was necessary to dispose a plurality of inductors in an amplifier for matching input impedance according to the passive filter theory. On the other hand, the more inductors are disposed in an amplifier, the higher noise figure is generated, and the bulky chip is also needed for installing plenty of inductors. Accordingly, it is difficult in chip designs and product applications.